Deontay Wilder will be offered two fights with Anthony Joshua, but promoter Eddie Hearn refused to rule out Wladimir Klitschko with a 'wild card in play' for a Wembley title defence.
Matchroom Boxing boss Hearn has been considering opponents for Joshua's next fight, with the unified heavyweight champion instructing him to make a fresh attempt to agree a deal with Wilder, who defends his WBC title against Tyson Fury in Los Angeles on December 1.
If Wilder successfully overcomes Fury, there is a three-week window to finally thrash out terms with the American's team for two fights between the rival belt holders.
"If Fury wins and the rematch clause kicks in, we know we've got to move on ourselves, but my instruction is 'Make that fight.'
"They haven't really wanted to speak to me before it. Now when the fight's over, if Wilder wins, we'll be on him on Sunday, saying any chance now? Can we meet now? If they say no again, I don't know what else we can do.
"If they are true to their word, on December 2, if they beat Tyson Fury, we will immediately start negotiations and we'll see where we get to. April 13 is easy, and it's a two-fight deal this time, the offer that we've made. One in America, one in the UK, we cannot say fairer than that.
"We've got to do our best to try and make it happen, and we'll be doing that straight after the fight. We've been trying to do it for the last two months, but no, wait, wait, wait.
"We'll wait and then we'll have a go on December 2, and we've probably got three weeks to make the fight. It's enough time, if everyone is sensible, but who knows whether they really want it deep down."
Wilder's co-manager Shelly Finkel told Sky Sports he remains willing to resume negotiations with Hearn.
"I have never rejected a call from Barry or Eddie," said Finkel. "My phone is always open to them."
Hearn confirmed that neither he or Joshua will attend the Wilder-Fury fight due to work and media commitments, but Wilder is still the No 1 target.
"We've got our show in Italy next Friday, and AJ goes out on Tuesday to film in America," said Hearn.
"He'll also be at the 'Canelo' fight with DAZN, and he'll be doing a lot of media stuff around there. Will he watch? Probably, yeah. I haven't really spoken to him about the fight that much. He's just focused on Deontay Wilder."
A rematch with Dillian Whyte is an alternative option, with Hearn also considering a 'wild card' opponent as speculation continues about Wladimir Klitschko and Andre Ward returning from retirement.
Hearn said: "People talk about Andre Ward, Wladimir Klitschko, who knows what could happen? But you can't just limit yourself to saying 'all eggs in one basket for Deontay Wilder, or Dillian Whyte', because he's got a very tough fight against Derek Chisora. Chisora and Haye are thinking 'we're going to beat Dillian Whyte and fight AJ ourselves.'
"Bernd Boente said 'It's not Wladimir Klitschko' and Wladimir said 'Hold on, don't talk for me, I'll talk for myself.' An April return, Wladimir Klitschko against Joshua, who knows? That would be what? Two years on from their first epic fight. One of the best heavyweight fights of all time. We'll see."